This invention relates to processing of blood samples. In particular, this invention relates to processing of whole blood samples to separate the cellular components in the blood samples from the liquid fractions.
Blood sample analyses are routinely performed to address a number of health concerns. Detection and/or quantitation of physiological compounds, for example, cholesterol, hormones, metabolites and the like can provide valuable information regarding the health of an individual. Generally, a blood sample is obtained from the patient at a health care facility such as a hospital, an emergency room and/or a physician""s office and sent to a clinical laboratory for further processing.
In order to analyze the blood sample for the desired compounds and/or analytes, the cellular components from the whole blood samples are generally separated from the plasma, i.e. the liquid fraction of the blood. The cellular components of blood include, for example, erythrocytes, leukocytes and platelets. The erythrocytes are the most abundant. Erythrocytes can also interfere with assays due to their chromogenic nature.
Centrifugation is most commonly performed as the first step in a blood sample analysis to separate the cellular, i.e. semi-solid components, from the liquid component of the blood. The centrifugation is generally performed in a clinical laboratory after the blood sample is transported from the blood sample acquisition site. After centrifugation, the liquid component, i.e. the plasma is generally used for the desired analysis. The analysis of plasma for the desired analytes is conducted in automated or semi-automated systems, for example, diagnostic analyzers.
The steps of acquiring the blood sample, sending it to a clinical laboratory and centrifuging the blood samples prior to the desired analysis has considerable setbacks. First, the process is labor intensive and time consuming. Second, these procedures can expose laboratory staff to hazards of infection from handling patients"" samples. In fact, several studies have shown that the lifetime risk of hepatitis B virus infection among health-care workers who have frequent contact with blood is between 15 and 30 percent or about 50-100 times the risk in the general population. (J. L. Dienstag, et al., Amer. J. Epidemiol., vol.115, pages 26-39, 1982 and B. S. Levy, et al., Amer. J. Epidemiol., vol. 106, pages 330-335, 1977) Transcription errors, specimen mix-ups and other mishandling are also common problems.
More recently, integrated blood-collection and processing systems have been introduced to serve the fully automated labs. A significant engineering effort has been invested in the development of sophisticated robust centrifuges that are needed to separate the blood cells in these large volume samples. The entire blood-processing and presentation process is highly labor-intensive and consumes more than 30 minutes. Thus, there is a great need for methodologies, protocols and equipment to effectively automate the blood sample preparation process in semi- and fully automated labs that are serving a wide variety of diagnostic instruments.
Sample centrifugation, usually at greater than 2000 revolutions per minute (rpm) for up to 10 minutes, is a step that affects the time to result. The analytical throughput of clinical analyzers can be limited by a lengthy preanalytical phase during which samples are prepared for analysis. Present sample processing procedures are limiting factors in fully realizing the high efficiencies potentially available with existing analytical instrumentation and are also slowing the delivery of test results at patient bed site, emergency room, and the like. These time consuming processes are also preventing the full implementation of physician-office diagnostics.
There is an increasing need for the ability to separate whole blood cellular components from the plasma of the blood sample at the blood sample acquisition site, i.e. in a physician""s office, an emergency room or a patient""s home. The plasma can then be used immediately, if desired, in a diagnostic test by the patient and/or the health care worker at the sample acquisition site, thus eliminating or reducing the use of clinical laboratory personnel for performing diagnostic tests.
A significant emphasis is currently being placed in the health care field related to the ability to provide desired results faster and in a more cost-efficient manner. Thus, procedures that eliminate or reduce the time required to conduct some of the labor-intensive steps can improve the time to result and reduce the costs.
In a first aspect, the invention pertains to a method for processing a blood sample to separate whole blood cellular components from plasma. The method includes contacting the blood sample with magnetically attractable particles associated with an agglutinating agent selected to bind to the whole blood cellular components in the blood sample. The method also includes subjecting the blood sample with the magnetically attractable particles to a magnetic field gradient to separate the magnetically attractable particles from the plasma.
In a further aspect, the invention pertains to a method for assaying a blood sample for the presence of one or more analytes. The method includes assaying an aliquot of plasma for the analyte or analytes. The method for obtaining the plasma includes processing the blood sample to separate the whole blood cellular components from plasma by contacting the blood sample with magnetically attractable particles associated with an agglutinating agent. The agglutinating agent is selected to bind to the whole blood cellular components in the blood sample but not the analyte or analytes being assayed. The method also includes subjecting the blood sample with the magnetically attractable particles to a magnetic field gradient to separate the magnetically attractable particles from the plasma.
In yet another aspect, the invention pertains to a device for processing a blood sample to separate the whole blood cellular components from plasma. The device includes a container having magnetically attractable particles associated with an agglutinating agent. The volume of the magnetically attractable particles in the container is selected such that when a magnetic field gradient is applied to a suspension of the particles, the particles accumulate in less than about 5 minutes at a surface of the container closest to the magnetic field gradient.
In a further aspect, the invention pertains to a reagent to separate whole blood cellular components from plasma in a blood sample. The reagent includes magnetically attractable particles associated with an agglutinating agent. The volume of magnetically attractable particles is selected to process a blood sample such that when the particles are in suspension, the particles are drawn away from the liquid of the blood sample in less than about five minutes when a magnetic field gradient is applied.